The present invention relates generally to flat panel displays and more particularly to solving outgassing problems with flat panel displays.
Cathode-ray tube (CRT) displays have been the predominant display technology for purposes such as home television and computer systems. For many applications, CRTs have advantages in terms of superior color resolution, high contrast and brightness, wide viewing angles, fast response times, and low manufacturing costs. However, CRTs also have major drawbacks such as excessive bulk and weight, fragility, high power and voltage requirements, strong electromagnetic emissions, the need for implosion and x-ray protection, undesirable analog device characteristics, and a requirement for an unsupported low internal pressure envelope that limits screen size.
To address the inherent drawbacks of CRTs, alternative display technologies have been developed. These technologies generally provide flat panel displays, and include liquid crystal displays (LCDs), both passive and active matrix, electroluminescent displays (ELDs), plasma display panels (PDPs), vacuum fluorescent displays (VFDs) and field emission displays (FEDs).
The FED offers great promise as an alternative flat panel display technology. Its advantages include low cost of manufacturing as well as the superior optical characteristics generally associated with the CRT display technology. Like CRTs, FEDs are phosphor based and rely on cathodoluminescence as a principle of operation. FEDs rely on electric field or voltage induced electron emissions to excite the phosphors by electron bombardment rather than the temperature induced electron emissions used in CRTs. To produce these emissions, FEDs have generally used row-and-column addressable cold cathode emitters of which there are a variety of designs, such as point emitters (also called cone, microtip, or xe2x80x9cSpindtxe2x80x9d emitters), wedge emitters, thin film amorphic diamond emitters, and thin film edge emitters.
Each of the FED emitters is typically a miniature electron gun of micron dimensions formed into the baseplate of the FED. A faceplate is merged with the baseplate and hermetically sealed so the FED will operate at a low internal pressure. The inside of the faceplate is coated with phosphors and a thin film of metal. When a sufficient voltage is applied between the emitter and an adjacent gate, electrons are emitted from the emitter over a relatively wide area. A focus plate focuses the electrons within a picture element, or pixel. The emitters are biased as cathodes and the thin film of metal is biased as an anode, which causes the emitted electrons to be attracted and accelerated to strike the phosphors on the faceplate. The phosphors then emit visible light, which form the pixels making up the image on the viewing surface of the FED.
Electron emissions in FEDs require a low internal pressure and that they be contaminant-free to avoid serious problems, such as pressure degradation, emission current degradation, and/or plasma generation or ionization which can lead to non-uniform brightness of the display, decrease display efficiency, and/or shortening of the working life of the display.
Many different approaches have been tried to maintain the low internal pressure and contaminant-free condition.
In one approach, the FED is hermetically sealed in air and then evacuated through a tube, which is pinched or melted shut after evacuation in a process called xe2x80x9ctipoffxe2x80x9d. To assist in the evacuation process and to maintain the low internal pressure, a xe2x80x9cgettering materialxe2x80x9d is used which absorbs contaminant gasses by various chemical reactions. The gettering material is deposited in a portion of the tube between the flat panel display and the pinch or melt point of the tipoff process. This process has the disadvantage of the tube being subject to breakage during the handling, which accompanies manufacturing.
Another approach is forming a getter at a location along the interior surface of a baseplate or/and faceplate. This is disadvantageous because a getter typically needs a substantial amount of surface area to perform the gas collection function and this approach significantly reduces the active-to-overall area ratio. In addition, the active components of the FED easily become contaminated during the gettering material deposition process and some of the active FED components could become short-circuited.
A still further approach uses a pre-fabricated getter unit placed closer to the actual display elements than gettering material in the tube but further than the getting material in the display area. Unfortunately, the pre-fabricated getter takes up room beside the FED.
For flat panel displays with these gettering systems, it has been determined that certain gasses remain and are difficult to remove by the gettering system even after long periods of time. Knowing that the contaminant gasses cause severe problems, those skilled in the art have long sought a system by which the gettering effect could be improved, but they have been unsuccessful.
The present invention provides a method for reducing operational outgassing of contaminant gasses in a flat panel display having a cathode carrying baseplate hermetically sealed to an anode-coated, phosphor-bearing, faceplate with a low internal pressure between the baseplate and the faceplate. It has been discovered that a great deal of the operational outgassing occurs during the first few hours of operation. By desorption processing of the flat panel display in a vacuum before hermetic sealing, it is possible to reduce operational outgassing. Without being limiting, three embodiments of the desorption processing are disclosed. The first involves plasma scrubbing, the second involves electron irradiation pre-aging, and the third involves electron irradiation pre-aging of the faceplate in an evacuation process. This desorption processing extends the life of the FED by an unexpected factor of at least two times.
The above and additional advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawings.